Boiling Performance of Graphene Oxide Coated Copper Surfaces at High Pressures

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Nanxi Li ◽  
Amy Rachel Betz
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Graphene Oxide ◽  
High Pressures ◽  
Oxide Coating ◽  
Dip Coating ◽  
Copper Surface ◽  
Oxide Surface ◽  
Rate Of Increase ◽  
Coated Surface

Graphene has been investigated due to its mechanical, optical, and electrical properties. Graphene's effect on the heat transfer coefficient (HTC) and critical heat flux (CHF) in boiling applications has also been studied because of its unique structure and properties. Methods for coating graphene oxide (GO) now include spin, spray, and dip coating. In this work, graphene oxide coatings are spray coated on to a copper surface to investigate the effect of pressure on pool boiling performance. For example, at a heat flux of 30 W/cm2, the HTC increase of the GO-coated surface was 126.8% at atmospheric pressure and 51.5% at 45 psig (308 kPa). For both surfaces, the HTC increases with increasing pressure. However, the rate of increase is not the same for both surfaces. Observations of bubble departure showed that bubbles departing from the graphene oxide surface were significantly smaller than that of the copper surface even though the contact angle was similar. The change in bubble departure diameter is due to pinning from micro- and nanostructures in the graphene oxide coating or nonhomogeneous wettability. Condensation experiments at 40% relative humidity on both the plain copper surface and the graphene oxide coated surface show that water droplets forming on both surfaces are significantly different in size and shape despite the similar contact angle of the two surfaces.

scholarly journals Optimization of Process Parameters for a Chemi-Absorbed Graphene Coating and Its Nano Tribological Investigation

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 55 ◽  
Author(s):  
Pengfei Li ◽  
Yuncheng Li ◽  
Hongyue Chen ◽  
Hui Liu ◽  
Xianhua Cheng
Keyword(s):  
Contact Angle ◽  
Graphene Oxide ◽  
Water Contact Angle ◽  
Coefficient Of Friction ◽  
Process Parameters ◽  
Self Assembly ◽  
Titanium Substrate ◽  
Oxide Coating ◽  
Water Contact ◽  
Hydrothermal Temperature

A reduced graphene oxide coating was deposited on a titanium substrate for potential anti-friction applications in nano- or micro-mechanical systems. A γ-aminopropyltriethoxysilane coating was self-assembled on the substrate as an adhesive interlayer beforehand. The process parameters of self-assembly and hydrothermal reduction of graphene oxide coating were explored via water contact angle and tribological tests. Insufficient self-assembly duration of graphene oxide layer can be detected by water contact angle results, and the corresponding coating displayed a higher coefficient of friction and shorter anti-wear lifetime than the optimized one. Proper hydrothermal temperature and duration were also confirmed by its water contact angle, coefficient of friction and anti-wear lifetime. Noticeably, excessive hydrothermal temperature or duration would reduce the coefficient of friction, but diminish the anti-wear resistance. The optimized process parameters were confirmed as assembly duration of graphene oxide coating for 12 h, hydrothermal reduction duration of 6–8 h at 135 °C. Nano tribological behaviors of the obtained hydrothermal reduced graphene oxide coating by AFM tester were then investigated under various testing circumstances. The results showed that the coating performed reliable and low adhesion and friction forces under all circumstances. The nanowear resistance of the titanium substrate was significantly strengthened by the prepared coating.

Effect of Wettability on Pool Boiling Incipience in Saturated Water

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Jinsub Kim ◽  
Seongchul Jun ◽  
Jungho Lee ◽  
Seong Hyuk Lee ◽  
Seung M. You
Keyword(s):  
Heat Flux ◽  
Life Cycle ◽  
Pool Boiling ◽  
Copper Surface ◽  
Contact Angles ◽  
Al2o3 Nanoparticles ◽  
Saturated Water ◽  
Boiling Incipience ◽  
Coated Surface ◽  
Bare Surface

Three different copper surfaces - bare, Al2O3 nano-coated, and Polytetrafluoroethylene (PTFE) coated - are prepared and tested to examine the effect of wettability on the pool boiling incipience in saturated water at 1 atm. A copper surface is coated with Al2O3 particles ranging 25~43 nm in diameter by immersing the surface in Al2O3/ethanol nanofluid (1g/l) and boiled for 3 min. SEM image in Fig. 1 shows the coated Al2O3 nanoparticles on the copper surface, together with the reference bare surface. PTFE coating is also applied to the copper surface using spin coating method with the mixture of Dupont AF 2400 particles and 3M FC-40 solvent. The final coating thickness of the PTFE coating is estimated to be 30 nm. The three surfaces exhibit different static contact angles, 78° (bare), 28° (nano-coated), and 120° (PTFE coated) in Fig. 2, respectively. Wettability affects the boiling incipience heat flux where initial bubble nucleation starts: 15 kW/m2 for the bare surface; 30 kW/m2 for the nano-coated surface; and 2.5 kW/m2 for the PTFE coated surface. Captured images from the high speed camera at 2,000 fps show significantly different bubble shapes and departure frequencies in Fig. 3. During the bubble growth, advancing contact angles are captured and shown qualitatively and found consistent with their static angle measurements for the sessile droplet observed at each surface. The larger bubble is generated on the nano-coated surface compared to that of the bare surface because improved wetting makes promising cavities flood and thus incipience is delayed, resulting in higher superheat. The single bubble life cycle appears to be much longer on the PTFE coated surface due to the increase of the contact angle which becomes hydrophobic (> 90°), resulting in lower bubble departure frequency. Successive tests at the same heat flux of 30 kW/m2 confirmed that life cycle on the PTFE coated surface (88.5 ms) is consistently longer than that on the bare surface (16.5 ms) and nano-coated surface (20 ms).

Critical Heat Flux of Graphene Coated Copper Surface at High Pressures

2015 ◽  
Author(s):  
Nanxi Li ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Pressures ◽  
Pool Boiling ◽  
Copper Surface ◽  
Test Fluid ◽  
System Pressure ◽  
Wall Superheat ◽  
Copper Cylinder

Boiling is an efficient way to transfer heat due to the latent heat of vaporization. Many variables, such as surface properties, fluid properties, and system pressure, will affect the performance of pool boiling. Enhanced pool boiling has extensive applications in chemical, microelectronics, and power industries. Previous research has shown that micro- or nanostructured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. Graphene as a very good material with superb mechanical and electrical properties also has potential to enhance pool boiling performance. The purpose of this research is to investigate heat transfer enhancement on a graphene coated surface compared to a plane copper surface at atmospheric pressure and increased pressures with deionized water. The effect of the graphene coating on the critical heat flux is also investigated. To carry out the experiments, we designed and fabricated a special experimental facility that will withstand the high pressures (up to 20 bar) and high temperatures. Graphene is coated on a 1 cm2 copper surface using spray coating. The boiling vessel is pressurized with nitrogen and the system pressure is controlled by a back pressure regulator. The test fluid is preheated to saturation temperature by two 500 W cartridge heaters. Multiple 150 W cartridge heaters are inserted in a copper cylinder to provide wall superheat for bubbles to nucleate on the studied surface. When the system reaches steady state, a process controller controls these cartridge heaters to increase the heat flux gradually from 0 kW/m2 to the critical heat flux. The copper cylinder is insulated with PTFE to minimize heat loss from the side. The gap between the copper cylinder and the insulation surface is carefully sealed with high temperature epoxy to reduce undesired nucleation sites. The wall superheat corresponding to each heat flux is extrapolated using Fourier’s law from three thermocouple readings. The heat transfer coefficient can thus be calculated at each heat flux for the every test fluid at its corresponding pressure. A camera with 3.2 cm field of view at a working distance of 12 cm to 15 cm is used to visualize the bubble formation on the heated surface.

scholarly journals Hydrophobic Modification of Graphene Oxide and Its Effect on the Corrosion Resistance of Silicone-Modified Epoxy Resin

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 89
Author(s):  
Wei Yuan ◽  
Qian Hu ◽  
Jiao Zhang ◽  
Feng Huang ◽  
Jing Liu
Keyword(s):  
Contact Angle ◽  
Corrosion Resistance ◽  
Graphene Oxide ◽  
Physical Properties ◽  
Epoxy Resin ◽  
Electrochemical Impedance ◽  
Salt Spray ◽  
X Ray ◽  
Modified Graphene Oxide ◽  
Modified Epoxy

This study modified graphene oxide (GO) with hydrophilic octadecylamine (ODA) via covalent bonding to improve its dispersion in silicone-modified epoxy resin (SMER) coatings. The structural and physical properties of ODA-GO were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle tests. The ODA-GO composite materials were added to SMER coatings by physical mixing. FE-SEM, water absorption, and contact angle tests were used to evaluate the physical properties of the ODA-GO/SMER coatings, while salt spray, electrochemical impedance spectroscopy (EIS), and scanning Kelvin probe (SKP) methods were used to test the anticorrosive performance of ODA-GO/SMER composite coatings on Q235 steel substrates. It was found that ODA was successfully grafted onto the surfaces of GO. The resulting ODA-GO material exhibited good hydrophobicity and dispersion in SMER coatings. The anticorrosive properties of the ODA-GO/SMER coatings were significantly improved due to the increased interfacial adhesion between the nanosheets and SMER, lengthening of the corrosive solution diffusion path, and increased cathodic peeling resistance. The 1 wt.% ODA-GO/SMER coating provided the best corrosion resistance than SMER coatings with other amounts of ODA-GO (including no addition). After immersion in 3.5 wt.% NaCl solution for 28 days, the low-frequency end impedance value of the 1 wt.% ODA-GO/SMER coating remained high, at 6.2 × 108 Ω·cm2.

scholarly journals Cold Plasma Deposition of Polymeric Nanoprotrusion, Nanoparticles, and Nanofilm Structures on a Slide Glass Surface

Processes ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 99
Author(s):  
Sun-Woo Yi ◽  
In-Keun Yu ◽  
Woon-Jung Kim ◽  
Seong-Ho Choi
Keyword(s):  
Contact Angle ◽  
Visible Light ◽  
Methyl Methacrylate ◽  
Cold Plasma ◽  
Plasma Deposition ◽  
Vinyl Monomers ◽  
Glass Slides ◽  
Structure Surface ◽  
One Step ◽  
Coated Surface

In this study, we coated the surface of glass slides with nanoprotrusion, nanoparticles, and nanofilm structures by one-step plasma deposition of three vinyl monomers. Three functional vinyl monomers with symmetrical polarity sites were used: methyl methacrylate (MMA), trifluoro methylmethacrylate (TFMA), and trimethylsilyl methyl methacrylate (TSMA). The TSMA/MMA (80/20, mol-%) nanoprotrusion-coated surface of slide glass was superhydrophobic, with a 153° contact angle. We also evaluated the transmittance (%) of the slide glass with nanoprotrusions in the infrared (IR) (940 nm), ultraviolet (365 nm) and visible light (380–700 nm) regions. The obtained nanoprotrusion structure surface of slide glass created by plasma deposition transmits more than 90% of visible light.

scholarly journals Eco-Friendly Reduced Graphene Oxide Nanofilter Preparation and Application for Iron Removal

Separations ◽  
2021 ◽  
Vol 8 (5) ◽  
pp. 68
Author(s):  
Pankaj Kumar Jha ◽  
Watsa Khongnakorn ◽  
Chamorn Chawenjkigwanich ◽  
Md Shahariar Chowdhury ◽  
Kuaanan Techato
Keyword(s):  
Contact Angle ◽  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Inductively Coupled Plasma ◽  
Membrane Filter ◽  
Water Flux ◽  
Water Filtration ◽  
Dimethyl Formamide ◽  
Reduced Graphene ◽  
Callistemon Viminalis

In this paper, the green synthesis of reduced graphene oxide (r-GO) nanomaterials using Callistemon viminalis leaf extract as a reducing and stabilizing agent is reported for the first time. The synthesized r-GO nanomaterials were characterized using UV–Vis, XRD, FE-SEM, TEM, and energy dispersive X-ray (EDX) analyses. The nanofilter membrane was prepared by varying the amounts of r-GO nanomaterials in a Polysulfone-N,N-dimethyl formamide (DMF) solution. The nanofilter membrane was characterized by the contact angle, atomic force microscopy (AFM), UV–Vis, and FTIR. The results confirm the formation of r-GO nanomaterials. Higher amounts of r-GO nanomaterials in the membrane show a lower contact angle, thus confirming their hydrophilic nature. Iron water filtration was performed with different amounts of r-GO nanomaterials in the membrane filter, and the water flux was smooth over an increased time period. Inductively Coupled Plasma (ICP) analysis showed a higher percentage of iron rejection (95.77%) when higher amounts (0.10 g) of r-GO nanomaterials were used in a mixed membrane (i.e., sample C). In conclusion, the findings illustrate that Callistemon viminalis mediates the synthesis of r-GO nanomaterials, which is useful in water filtration, and can be incorporated into membrane filters, since it removes iron.

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